Performance of the Zweymüller total hip arthroplasty system: a literature review including arthroplasty register data

Differences in periprosthetic bone mineral density tendencies with Types 1 and 3C stems in bipolar hemiarthroplasty following hip fracture

The purpose of this study was to compare the periprosthetic bone mineral density (BMD) changes in the patients who underwent bipolar hemiarthroplasty (BPHA) for geriatric femoral neck fracture between two major different types of cementless femoral stems. A total of 93 patients (96 hips) who underwent BPHA for femoral neck fracture were categorized into two groups: Type 1 (42 patients, 44 hips), and Type 3C stem (51 patients, 52 hips). We investigated the annual follow-up trends of periprosthetic BMD at each Gruen zone during minimum postoperative 5-years; moreover, we compared the trends of periprosthetic BMD between both groups. The mean follow-up period was 7.1 years. In both groups, the overall BMD at the last follow-up had decreased compared with the baseline. In those with the Type 1 stem, BMD in the lateral femoral meta-diaphysis significantly decreased at 1-year follow-up after surgery. In those with Type 3C stem, BMD in the lateral femoral metaphysis postoperatively decreased after 3-years, whereas the BMD in the mediolateral femoral diaphysis drastically decreased postoperative 1-year period and plateaued thereafter. Different tendencies according to stem design were observed obviously in the postoperative BMD change of the proximal femur in patients who underwent BPHA for geriatric femoral neck fracture.

Quality of outcome data in total hip arthroplasty: comparison of registry data and worldwide non-registry studies from 5 decades

PURPOSE

This systematic review assessed evidence on outcome (revision rate for all reasons) following hip arthroplasty from its beginning 5 decades ago.

METHODS

We evaluated all studies from all current hip implants since their market introduction in 1962 regarding "revision rate per 100 observed component years". Data were compared with arthroplasty registries.

RESULTS

A total of 54 different hip implants were included: for 81% (44 of 54) data is either absent or poor; for 30% (16 of 54) not a single publication could be found. For 52% (28 of 54) less than 100 revisions for all reasons are published in non-registry studies. The remaining 10 implants (19%) comprise 92638 primary implants with 4473 revisions. Control group were the same implants with 111658 primary cases and 3029 revisions from arthroplasty registries. A systematic developer bias as in knee arthroplasty could not be found but several independent authors were found to significantly bias the literature. The overall revision rates per 100 observed component years from non-registry studies (and joint registries) are 0.4 (0.5) for stems, 0.7 (0.7) for cups and 1.4 (2.1) for resurfacing systems.

CONCLUSIONS

For 81% of all hip implants assessed limited evidence exists from non-registry studies regarding outcome (revision rate) even 5 decades after market introduction. For the remaining 19% of implants no systematic developer bias could be found but several individual authors significantly biased results of single implants. We therefore ask for a more active publication of new implants.

Good mid- to long-term THA outcomes with a modified cementless rectangular biconical stem design

PURPOSE

Second- and third-generation cementless Zweymüller stems have achieved good long-term outcomes in total hip arthroplasty (THA). The PPF cementless proximal press-fit femoral stem (Biomet Inc.) is based on the Zweymüller stem, with some prominent design differences. This study was designed to assess its performance in terms of survivorship, clinical function, and radiographic outcomes.

METHODS

We retrospectively analysed 250 patients (303 hips) who underwent THA between 1998 and 2011. Patients attended a follow-up visit a mean 10.9 ± 2.6 years after the procedure. All patients underwent radiographic examination and were clinically assessed for Forgotten Joint Score (FJS) and pain visual analogue scale (VAS). Survivorship was calculated using Kaplan-Meier analysis.

RESULTS

Clinical data were available for 142 patients (192 hips) and radiographic data for 79 patients (109 hips). Stem survival was 99.1% (95% confidence interval [CI] 96.6%-99.8%) at 10 years and 95.6% (95% CI 96.6%-99.8%) at 15 years. The median postoperative FJS was 91 (interquartile range [IQR], 75-100). The median VAS score was 0 (IQR, 0-2). Radiolucent lines were observed in 47 hips (43.1%). 25 hips (22.9%) had Grade I ossification, 17 (15.6%) Grade II, and 2 (1.8%) Grade III. 12 hips (11.0%) had osteolysis in at least 1 femoral zone.

CONCLUSIONS

The cementless proximal press-fit femoral stem was associated with good mid- to long-term survival and functional outcomes. The current design can be considered equivalent to the second- and third-generation Zweymüller stems.

Radiological identification of Zweymüller-type femoral stem prosthesis in revision cases

INTRODUCTION

Since 1979 the number of patients treated with femoral stems has continued to grow, as well as the number of stems with features similar to the Zweymüller prosthesis produced by different companies. Identification can be problematic in case requiring revision. In the present paper, we present an overview of morphometric differences between the different stem designs, which can be useful for radiologic identification in revision cases.

METHODS

By doing some research on the Internet of specialized sites and worldwide literature, we searched for all femoral stems agreeing with Zweymüller principles (cementless, straight, tapered, rectangular cross-sectioned femoral stems).

RESULTS

We found 26 different stems from different companies producing or having produced in the past the Zweymüller-type femoral stems for hip prosthesis.

DISCUSSION

Accurate preoperative identification of the Zweymüller femoral stem type may be of critical importance to eventual outcomes following revision surgery. Each manufacturer has different instruments specific to the removal of their primary implants, and ensuring they are available can simplify the revision procedure significantly. Exact pre-operative planning is also necessary for selecting the correct ball head in cases where a stem is well-fixed and can be left in situ. The commonly used notation "Eurocone 12/14" provides no information about the actual taper angle. Whenever the stem is left in situ, the exact specifications of the taper must therefore be obtained from the manufacturer in order to use a metal sleeve that precisely fits it and the ball head. Failure to do so may result in severe complications, such as metallosis. In cases where it is not possible to identify the taper angle, the surgeon may even consider removal of the stem, though this significantly increases the surgical procedure's invasiveness. Only a single, uniform standard taper, such as that offered until 1994 by CeramTec, can solve these issues in the future.

CONCLUSION

The survival rate of the Zweymüller stems after ten years was 96 % and the complication rate was very low. Pre-operative identification of the femoral implant is of considerable importance for planning and correctly implementing revision procedures.

Long-term follow-up of primary total hip arthroplasty with the Alloclassic Variall system

PURPOSE

The aim of the present study was to evaluate the clinical and radiographic results of primary total hip arthroplasty (THA) performed with the Alloclassic Variall system (a modified version of the Alloclassic Zweymüller system) and to compare them with those in the literature for the original system.

METHODS

Between January 2001 and December 2002, 273 consecutive primary THAs were performed in 259 patients at a single centre with the study system, using ceramic-on-ceramic (81.7 %) or ceramic-on-highly-crosslinked-polyethylene (18.3 %) articulations.

RESULTS

At the time of this study, 28 patients (29 hips; 10.6 %) had died and 40 (43 hips; 15.8 %) were lost to follow-up. Seventeen patients (19 hips; 7.0 %) could be reached only by telephone. There were four revisions in four patients (1.5 %), all involving only the femoral component. Ten-year Kaplan-Meier survival with revision of any component for any reason as the endpoint was 98.4 % (95 % confidence interval: 96.9-100 %; 30 hips remained 'at risk'). A total of 170 unrevised patients (178 hips; 65.2 %) were assessed clinically and radiographically at a median follow-up of 9.3 years (interquartile range [IQR] 8.8-9.8 years). The median Harris hip score (HHS) was 99.9 points (IQR 97.7-100). The score did not differ significantly between the two articulations. There was no sign of radiographic loosening.

CONCLUSIONS

The ten-year implant survival and the HHS score outcomes for THAs performed with the novel system were in line with those documented in the literature for its predecessor.

Impact of implant developers on published outcome and reproducibility of cohort-based clinical studies in arthroplasty

BACKGROUND

The reproducibility of the results of cohort-based clinical studies of arthroplasty procedures by the average orthopaedic surgeon is a major issue involving the quality of the scientific literature. We compared the results of a comprehensive literature analysis with data from national arthroplasty registries to examine the influence of arthroplasty implant inventors on the outcomes published in peer-reviewed journals.

METHODS

A structured review of the literature published in MEDLINE-listed journals was performed. A comparison of the average revision rates in the identified studies (adjusted for the number of arthroplasty cases and the duration of follow-up) with the registry data was then conducted.

RESULTS

Seventeen of the analyzed arthroplasty implants were developed in the United States. Studies by the developers of these implants often had a substantial influence on the published outcome. For approximately 50% of the implant systems analyzed, the average revision rate derived by combining all published studies showed a statistically significant and clinically relevant deviation from the revision rate derived from the arthroplasty registry data, which reflected the outcome in the average patient. For the majority of implants for which the revision rate calculated from the published clinical studies was very low compared with the rate calculated from the registry data, the developing institution accounted for 39% to 100% of the published outcome data for the implant. In contrast, the published results were usually reproducible in clinical practice if <25% of the published data were reported by the developers. Three of the nine arthroplasty implants developed in Europe showed a significant and clinically relevant difference between the revision rate derived from only the studies published by the developers and the rate calculated from the registry data. However, because of the considerably greater amount of data from independent studies that was typically available for the European implants than for the American implants, studies by the developer that deviated significantly from the registry data could usually also be identified as outliers by a meta-analysis of all published studies. A high proportion of the published data involving three of the European implants was reported by the inventors, but comparison with the registry data revealed that the average published revision rates for two of these three implants were reproducible in clinical practice.

CONCLUSIONS

The published results of the clinical studies involving many of the arthroplasty implants, especially implants developed in the United States, were highly influenced by reports from the center that developed the implant. This often had a substantial effect on the reproducibility of the outcome data. There appeared to be relevant differences between the medical research systems in Europe and the United States that also affected the reproducibility and applicability of the results for the average surgeon. Registry data can contribute substantial added value to an informed discussion of arthroplasty outcomes.

The outcome of the cementless tapered SL-Plus stem: an analysis of arthroplasty register data

PURPOSE

The aim of this study is to evaluate the outcome of the cementless SL-Plus stem in worldwide arthroplasty register datasets.

METHODS

A structured analysis was conducted the registered data about the SL-Plus stem manufactured by Smith&Nephew including published data from Australia as well as previously unpublished datasets from the Registers of Lombardia, Italy and Valdoltra, Slovenia. A total of 75% of the data analysed had not been published so far. The primary outcome measure was the revision rate, calculated in revisions per 100 observed component years. We evaluated a total of 10,684 primary and 122 revision surgeries with an average follow-up period of four years.

RESULTS

All datasets showed good and reproducible results for treatment with the SL-Plus stem. An average of 0.31 revisions per 100 observed component years had been reported, which is considerably below the worldwide average (1.29) found for total hip arthroplasty independent of the product. The results of a large centre did not essentially deviate from the revision rates in Lombardia, where the numbers of cases per department are relatively low on average.

CONCLUSIONS

There were no indications for product defects or relevant errors in application. The SL-Plus stem can be considered a high-quality product that ensures good results also in the hands of less experienced surgeons. Data from even young registers can substantially contribute to the assessment of implants, even with the short follow-up periods. These datasets particularly allow for valid assessment of safety issues and can therefore make an essential contribution to the solution of problems of current relevance.